The original poster may eventually want to experiment with server side rendering or splitting their single page app into multiple apps, and hash URLs pretty much trap you into a single page app with client side routing.

That said, I didn't mean to cast a negative light on them. Using hash URLs makes it easy to build an app that can be reverse proxied to different hostnames and paths without content rewriting (to change the base tag's url for example), and it works well with legacy browsers.